This invention relates to agricultural or off-road tires. More particularly to high aspect ratio tires in that field.
Pneumatic tires generally have a tread overlaying a casing. The casing includes a belt or breaker structure. The carcass has at least one cord reinforced ply anchored to two annular substantially inextensible beads.
In radial tires, the carcass has at least one radial ply. In bias tires the carcass has at least two plies of equal but opposite orientation. In both cases the belts of radial tires or the breakers of bias tires prevents or restrict the growth of the tire when inflated. In automobile and truck tires, the ratio of section height divided by section width is usually much less than 95%, typically, in the range of 35% to 85%.
Agricultural or off-road vehicles generally have similar aspect ratios below 95%. In order to increase the load carrying capacity of such tires designers generally have required increasing the width of the tire while maintaining the same nominal rim diameter or simply increasing the tires overall size generally. This is so because the load carrying capacity of these tires is related to the air chamber capacity at a given inflation pressure. Another way to increase load carrying capacity is to increase the tire inflation pressure. This solution is commonly practiced in aircraft and earthmover and heavy construction equipment tires where the inflation pressure is up to 300 psi.
In agricultural tires, it is desirable to operate the tires at low pressure. This enables the tire to reduce soil compaction while improving the drawbar traction. In such a case, it is necessary to increase the air chamber volume to increase load capacity. This has meant in the past, increasing the tires section width, but wide tires means reduced crop yields once the crop is planted. One solution has been the development of narrow row crop tires. Such a tire is shown in U.S. design patent. These tires are narrow in width and have an aspect ratio up to 95%.
The inventors of the present invention have discovered that the use of ultra high aspect ratio agricultural or off-road tires can provide increased load carrying capacity at reduced operating pressures while increasing the tractive efficiency of the vehicle.
One of the objectives of the invention is to provide a pneumatic tire that can simulate the traction performance of tracked vehicles.
Another objective is to provide a ire having a reduced spring rate and improved vibration damping characteristic resulting in a softer ride performance tire. The objects being satisfied by the inventive tire described below.
An agricultural or off-road tire 20 for the drive axle or axles of a vehicle, is disclosed. The tire has an axis of rotation, a nominal rim diameter NRD of 20 inches or greater, and a carcass 21. The carcass 21 has at least one cord reinforced ply 22 and a pair of annular bead cores 24. A tread 32 is disposed radially outward of the carcass 21.
The tire 20 has an aspect ratio of greater than 95%, preferably 100% or greater most preferably greater that 100%.
The tire 20 has a contact patch when the tire is inflated to less than 16 psi and loaded on a hard flat surface, the contact patch having an axial width X and circumferential length of Y, wherein the ratio of Y/X is at least greater than 1.0. Preferably the contact patch has a leading end and a trailing end; the distance between the leading and trailing end defines the circumferential length Y. The tire 20 when inflated to less than 16 psi and normally loaded has a first radial line intersecting the leading end and a second radial line intersecting the trailing end.
The tire can have a carcass having one or more radial plies and a belt reinforcing structure between the ply or plies and the tread. Alternatively, the carcass can have two or more bias plies and a breaker structure between the tread and the bias plies.
The tread has a plurality of lugs spaced between a pair of lateral edges. Each lug has a radially outer contact surface area, the sum of the radially outer contact surface areas between the lateral edges as measured around the total circumference of the tire divided by the area between the lateral edges around the total tires circumference is less than 40%, preferably less than 30%.
xe2x80x9cAspect ratio,xe2x80x9d means the ratio of its inflated section height to its inflated section width.
xe2x80x9cAxialxe2x80x9d and xe2x80x9caxiallyxe2x80x9d means the lines or directions that are parallel to the axis of rotation of the tire.
xe2x80x9cBeadxe2x80x9d or xe2x80x9cBead Corexe2x80x9d means generally that part of the tire comprising an annular tensile member, the radially inner beads are associated with holding the tire to the rim being wrapped by or anchored to ply cords and shaped, with or without other reinforcement elements such as flippers, chippers, apexes or fillers, toe guards and chafers, the bead or beads under the tread being encapsulated in tread rubber can be with or without other cord reinforced fabric elements.
xe2x80x9cBelt Structurexe2x80x9d or Reinforcing Beltsxe2x80x9d means at least two annular layers or plies of parallel cords, woven or unwoven, underlying the tread, unanchored to the bead, and having both left and right cord angles in the range from 17xc2x0 to 27xc2x0 with respect to the equatorial plane of the tire.
xe2x80x9cBias Ply tirexe2x80x9d means that the reinforcing cords in the carcass ply extend diagonally across the tire from bead-to-bead at about a 25-65xc2x0 angle with respect to the equatorial plane of the tire, the ply cords running at opposite angles in alternate layers.
xe2x80x9cCarcassxe2x80x9d means a laminate of tire ply material and other tire components cut to length suitable for splicing, or already spliced, into a cylindrical or toroidal shape. Additional components may be added to the carcass prior to its being vulcanized to create the molded tire.
xe2x80x9cCircumferentialxe2x80x9d means lines or directions extending along the perimeter of the surface of the annular tread perpendicular to the axial direction.
xe2x80x9cDesign Rimxe2x80x9d means a rim having a specified configuration and width. For the purposes of this specification, the design rim and design rim width is as specified by the industry standards in effect in the location in which the tire is made. For example, in the United States, the design rims are as specified by the Tire and Rim Association. In Europe, the rims are as specified in the European Tyre and Rim Technical organization-Standards Manual and the term design rim means the same as the standard measurement rims. In Japan, the standard organization is The Japan Automobile Tire Manufacturer""s Association.
xe2x80x9cDesign Rim Widthxe2x80x9d is the specific commercially available rim width assigned to each tire size and typically is between 75% and 90% of the specific tire""s section width.
xe2x80x9cEquatorial Plane (EP)xe2x80x9d means the plane perpendicular to the tire""s axis of rotation and passing through the center of its tread.
xe2x80x9cFootprintxe2x80x9d means the contact patch or area of contact of the tire tread with a flat surface at zero speed and under normal load and pressure.
xe2x80x9cInnerxe2x80x9d means toward the inside of the tire and xe2x80x9couterxe2x80x9d means toward its exterior.
xe2x80x9cLateral Edgexe2x80x9d means the axially outermost edge of the tread as defined by a plane parallel to the equatorial plane and intersecting the outer ends of the axially outermost traction lugs at the radial height of the inner tread surface.
xe2x80x9cLeadingxe2x80x9d refers to a portion of part of the tread that contacts the ground first, with respect to a series of such parts or portions, during rotation of the tire in the direction of travel.
xe2x80x9cNet-to-gross Ratioxe2x80x9d means the ratio of the tread contacting surface area of the normally loaded and inflated tire to the total area of the tread, including non-contacting portions such as grooves as measured around the entire circumference of the fire.
xe2x80x9cNormal Inflation Pressurexe2x80x9d means the specific design inflation pressure and load assigned by the appropriate standards organization for the service condition for the tire.
xe2x80x9cNormal Loadxe2x80x9d means the specific design inflation pressure and load assigned by the appropriate standards organization for the service condition for the tire.
xe2x80x9cRadialxe2x80x9d and xe2x80x9cradiallyxe2x80x9d means directions radially toward or away from the axis of rotation of the tire.
xe2x80x9cRadial Ply Tirexe2x80x9d means a belted or circumferentially-restricted pneumatic tire in which the ply cords which extend from bead to bead are laid at cord angles between 65xc2x0 and 90xc2x0 with respect to the equatorial plane of the tire.
xe2x80x9cSection Height (SH)xe2x80x9d means the radial distance from the nominal rim diameter to the outer diameter of the tire at its equatorial plane.
xe2x80x9cSection Width (SW)xe2x80x9d means the maximum linear distance parallel to the axis of the tire and between the exterior of its sidewalls when and after it has been inflated at normal pressure for 24 hours, but unloaded, excluding elevations of the sidewalls due to labeling, decoration or protective bands.
xe2x80x9cTire Design Loadxe2x80x9d is the base or reference load assigned to a tire at a specific inflation pressure and service condition; other load-pressure relationships applicable to the tire are based upon that base or reference.
xe2x80x9cTrailingxe2x80x9d refers to a portion or part of the tread that contacts the ground last, with respect to a series of such parts or portions during rotation of the tire in the direction of travel.
xe2x80x9cTread Arc Width (TAW)xe2x80x9d means the width of an arc having its center located on the plane (EP) and which substantially coincides with the radially outermost surfaces of the various traction elements (lugs, blocks, buttons, ribs, etc.) across the lateral or axial width of the tread portions of a tire when the tire is mounted upon its designated rim and inflated to its specified inflation pressure but not subject to any load.
xe2x80x9cTread Widthxe2x80x9d means the arc length of the tread surface in the axial direction, that is, in a plane parallel to the axis of rotation of the tire.
xe2x80x9cUnit tread Pressurexe2x80x9d means the radial load borne per unit area (square centimeter or square inch) of the tread surface when the area is in the footprint of the normally inflated and normally loaded tire.